Television apparatus responsive to a transmitted color reference signal

ABSTRACT

A color reference signal is inserted during the vertical blanking interval of a transmitted television waveform, for utilization by The described apparatus in automatically setting the hue and saturation of the display of an NTSC or PAL receiver. The apparatus responds to the transmitted burst signal to lock the frequency of the sub-carrier oscillator of the Receiver and to the transmitted reference signal to adjust the phase of its oscillations.

FIELD OF THE INVENTION

This invention relates to color television receivers and, moreparticularly, to such apparatus as is capable of utilizing a referencesignal inserted in the vertical blanking interval of a transmittedtelevision waveform to improve the consistency of reproduced color.

Summary of the Invention

As will become clear hereinafter, apparatus constructed in accordancewith the invention responds to this insertion of the reference signal toprovide both automatic hue and saturation correction. As far as huecontrol is concerned, it will be seen that the reference signal isrecovered at the receiver to control the phase of its sub-carrieroscillator, while the transmitted color burst signal is recovered andused to lock the oscillator in frequency. Because the reference signalis of much longer duration than the burst, it is substantially lesssubject to phase variations from such phenomena as standing waves andmultipath, for example. Using the reference signal instead of the burstsignal then provides a tighter control over the phase of the oscillatorand improved color demodulation. Use of the periodically recurring burstto independently control the oscillator frequency, on the other hand,provides the apparatus with a speed of response and with asignal-to-noise ratio comparable to those exhibited by typical frequencyand phase control arrangements where the burst signal alone is employedto set the oscillator as the reference against which the demodulationoccurs.

As far as saturation control is concerned, it will be seen that theapparatus of the invention resembles known designs in developing anautomatic chroma control signal to set the chrominance channel gain.However, instead of following the typical approach of using theamplitude of the color burst as the reference for maintaining a constantchrominance level, the described apparatus will be seen to operate witha pedestal of the recovered reference signal serving as the means forcomparison. By selecting this pedestal of luminance amplitude andperforming the comparison within one of the receiver's color matrixamplifiers, for example, any change in contrast control setting willthen produce a corresponding change in the pedestal amplitude and anoverall adjustment in the chrominance gain. Automatic tracking betweenthe chrominance and luminance channels will then be automaticallyachieved. In addition, such focusing on the pedestal as the reference inmaintaining the chrominance gain instead of the color burst amplitudesubstantially reduces the previous difficulties in stabilizing theamplitude of the chrominance signal due to the cumulative tolerancesassociated with the burst signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention will become more clearlyunderstood from a consideration of the following description taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates a complete line within the vertical blanking intervalof a transmitted television waveform, including a reference signalusable in accordance with the present invention;

FIG. 2 illustrates, by way of a block diagram, one arrangement whichmight be employed in transmitting the reference signal together with astandard color television broadcast signal; and

FIG. 3 illustrates, also by way of block diagram, apparatus responsiveto such reference signal for achieving automatic hue and saturationcorrection in the receiver to improve the quality and consistency ofreproduced color images.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a preferred format for the color reference signalinserted into the transmitting waveform--for example, at line 20 of thevertical blanking interval of each television field. As shown, the lineinterval extends from time T₁ to time T₂, with a conventional horizontaldeflection synchronizing pulse A of 40 IRE units amplitude extending inthe negative direction at the beginning of the line. The pulse A isfollowed by a synchronizing burst B of color sub-carrier frequency(3.579545 MHz) and of --(B-Y) phase. The burst B, having a peak-to-peakamplitude of 40 IRE units, is superimposed upon a blanking pedestal Cwhich, together with the burst and horizontal synchronizing pulse, formsa part of the conventional color television signal and, thus, need notbe described further.

The remainder of the line interval includes a first burst D of a fewcycles of lower frequency (for example, 0.5 MHz) followed by a secondburst E of comparable amplitude but of sub-carrier frequency ofpredetermined --(R-Y) phase. Such burst E is superimposed upon aluminance pedestal F of some 50 IRE units in amplitude, with the peakamplitude of this burst being approximately 44 IRE units. Such selectionfor this second burst amplitude follows a realization that the gain ofthe chrominance channel to a signal of --(R-Y) phase is of the order of1.14 and that automatic chroma control can be attained through acomparison of the amplitude of this second reference burst E after itsincrease by this factor (after demodulation) with the luminance level of50 IRE units. For a sub-carrier burst E of --(B-Y) phase, on the otherhand, the peak amplitude would generally be of the order of 25 IRE unitssince the receiver gain for such sub-carrier phase is approximately2.03. The insertion of the lower frequency burst D (which is optional)can be used to facilitate the gating of the reference burst E from thecomposite signal, and is at a frequency which is a compromise betweenthe maximum information which can be transmitted in the shortest periodof time and the Q required to separate the reference signal.

While the color reference signal E of the present invention may beinserted into the vertical interval at almost any point in the broadcastcommunication link between the camera and the receiver, the arrangementof FIG. 2 illustrates its insertion at the transmitting end. Thus, thereis shown a conventional color television camera 11 which provides at itsoutput leads simultaneous red "R," green "G," and blue "B" color videosignals which are applied to the input terminals of a colorplexer 13 ofappropriate design. Such colorplexer unit receives the simultaneouscolor video signals and synchronizing and blanking signals from asynchronizing generator 15, and produces luminance and chrominancesignals through the agency of suitable modulating and matrix circuits.The luminance and chrominance signals as thus furnished by thecolorplexer 13 are applied via a lead 17 to the transmission facilitiesrepresented by the block 19. The color reference signal generatorproviding the waveform of the type shown in FIG. 1 is indicateddiagrammatically by a block 21 in FIG. 2, with the output signal of thegenerator being added to the composite broadcast signal at the inputlead 17 of the transmission facility. It will also be noted from FIG. 2that the reference signal generator 21 receives, at its input terminals,horizontal and vertical drive pulses from the synchronizing generator 15together with a color sub-carrier wave. The sub-carrier wave may bederived from the same source as that which supplies the sub-carrier waveto the colorplexer apparatus, in order to insure a locked relationbetween the color reference signal burst of the vertical blankinginterval and the color television signal synchronizing burst on the backporch portion of the horizontal pulse.

The transmission facility represented by the block 19 will be understoodas including any of the usual signal conveying links normally employedin commercial broadcast systems. Completing the illustration of thesystem is a receiver 23 which serves to reproduce the televised imagefrom the composite signal applied to its input terminal via thetransmission facility, and on whose image display device will appear thereproduced image corrected as to hue and saturation by the apparatus ofthe invention, now to be described.

The apparatus of FIG. 3 is useful in an R-Y and B-Y low-leveldemodulating system in which 90° phase separation is present between thesub-carrier signal coupled from the receiver's reference oscillator 50to the R-Y and B-Y demodulators 52, 54. The output signals from thesedemodulators are respectively applied to a pair of matrix and amplifiercircuits 56 (red), 58 (blue) for combination with a luminance or Ysignal applied to an additional input thereof--from, for example, thefirst video stage of the receiver. The output signals from the matrixcircuits 56, 58 are applied to appropriate electrodes of a cathode-raykinescope (not shown), to form--with a green signal recovered from thered and blue information--the reproduced image in full color. Asindicated, the composite video signal is coupled from input terminal 60to the individual demodulator circuits 52, 54 by means of a chromaamplifying system 62 which sets the frequency response for thechrominance channel.

In accordance with the present invention, the synchronizing burstportion of the composite signal (B, in FIG. 1) is employed to lock thefrequency of the reference oscillator 50 but not its phase. In thisrespect, the apparatus of the invention in part distinguishes fromapparatus previously utilized in the prior art. To this end, thecomposite video signal applied at terminal 60 is coupled to a burstamplifier 64 which is keyed by a gate pulse supplied from the deflectionand high voltage circuitry of the receiver, to separate the colorsynchronizing bursts from the remainder of the composite waveform. Theseparated bursts are applied by a relatively large value couplingcapacitor 66 to the reference oscillator 50 to lock the frequency of theoscillator to that of the received burst signal. Because the burst istransmitted at the rate of once every television line, this capacitivecoupling acts as a short circuit to the burst, and rapidly couples it tolock the oscillator 50 in proper frequency. Such a periodicallyrecurring burst thus provides the apparatus with a speed of responsewhen switching between channels comparable to that exhibited in knownNTSC and PAL receiver systems where the color synchronizing burst isemployed to additionally lock the phase of the reference sub-carrieroscillator, as well. As will be readily appreciated.[., this alternatingcurrent coupling of the synchronizing bursts to the oscillator 50 hassubstantially little effect on the steady state phase of itsoscillations, as this is governed by the direct voltage on theoscillator reactance device. However--and in accordance with the presentinvention--such control over the reactance device is effected by thetransmitted reference signal (E, in FIG. 1), in combination with adirect current coupling to the reactance control.]. .Iadd.afterconsideration of the to-be-described closed loop control of the phase ofthe oscillator output in accordance with the transmitted referencesignal (E, in FIG. 1), that the phase of the oscillator output is lockedto the phase of said reference signal; in those instances where there isa sustained difference between the phase of the burst and the phase ofthe reference signal, the differing phase of the bursts will havesubstantially little effect on the steady state phase of the oscillatorwhich will be locked to the phase of the reference signal by the actionof a reference signal responsive control voltage DC coupled to theoscillator reactance device.Iaddend..

This phase-locking of the oscillator 50 to complete the hue controlaspect of the present invention is attained by sampling the output ofthe B-Y demodulator 54 during the vertical blanking interval in whichthe color reference signal is inserted. Because the color referencesignal is inserted at --(R-Y) phase, the output of the demodulator 54should nominally be zero when the reference signal phase and oscillatorphase are the same. Should any difference exist between these twophases, a correction voltage will be developed to adjust the oscillatorphase until the detected B-Y component is reduced to zero, at which timethe oscillator phase will lie along the R--Y axis.

Such automatic phase control action is achieved in the apparatus of FIG.3 first, through the use of a gate and clamp circuit 68 coupled toreceive the output of the B-Y demodulator 54 after amplification in anamplifier unit 70. Control of the gate 68 is, in turn, controlled by thesecond operative circuits associated with this phase control, namely anamplitude detector 72, a delay circuit 74 and a coincidence gate 76. Inparticular, these units 72-76 cooperate to provide a clamp pulse duringthe vertical blanking interval in which the color reference signal isinserted, by coupling the amplitude detector 72 to receive the processedsignal output of the chroma amplifying system 62 and by applying its ownoutput, in turn, to the coincidence gate 76 along with a pulse timed tocoincide with the blanking position of interest--shown as beingdeveloped by the delay circuit 74 counting down to the appropriate lineinterval in response to an applied vertical synchronizing rate pulse.The output of the gate circuit 68 will be understood as being directcurrent coupled to the reactance device of the oscillator 50, andprovides an oscillator phase control for color reference signals E toreduce the detected B-Y component towards zero. As will be seen, suchcontrol is independent of the phase of the color synchronizing burst B.

This usage of a color reference signal to establish the hue of areproduced color image represents a significant improvement over knownNTSC designs as the reference signal is far less susceptible to phaseshift errors due to its significantly longer duration than the colorsynchronizing burst. Thus, where the reference signal might occupy a 24microsecond or so time interval and multipath conditions may be such asto introduce a 2.5 microsecond delay, only a 0.1 radian phase changewould tend to be exhibited by large area chrominance information,whereas such display would be substantially influenced and affected ifthe same delay were present and the 2.5 microsecond burst were itselfused to provide the phase control.

However, the use of this burst signal to separately lock the frequencyof the sub-carrier oscillator of the receiver is advantageous--not onlybecause of its maintaining a comparable speed of operating response--,but because it enhances the exhibited signal-to-noise ratio over thatwhich would be exhibited if only the reference signal were employed forthe hue correction. This follows from the periodic recurrence of thesynchronizing burst every television line, as compared to the presenceof the color reference signal only once each television field. .[.Suchsingular use.]. .Iadd.Use .Iaddend.of a reference signal to correct thehue of a reproduced image is disclosed in U.S. Pat. No.3,456,068-Wilhelmy, the described apparatus of which .[.suffers thedisadvantages of slow response and poor signal-to-noise ratio improvedupon by the concurrent use of the color synchronizing burst as hereindescribed.]. .Iadd.makes use of a reference signal which occurs during asmall portion of image display intervals.Iaddend..

The apparatus of FIG. 3 further represents an improvement over theconstruction suggested by the aforementioned patent in that provision isadditionally made to use the same color reference signal for control ofthe saturation of the reproduced color display. To this end, a secondgate and clamp unit 78 is included, having a first input coupled tosense the output of the red matrix 56 and a second input controlled bythe clamp pulse generated by the combined actions of the units 72-76. Aswith the B-Y demodulator 54 for phase control, the output of the matrix56 will ideally be zero during the blanking interval insertion of thereference signal. The reason for this is that with a reference signal of--(R-Y) phase and with the pedestal upon which the reference bursts aresuperimposed having an amplitude equal to the luminance signal, theoutput of the R-Y demodulator 52 will comprise a pulse having anamplitude equal in magnitude but opposite in polarity to that of theluminance component of the composite video signal. With such componentbeing applied to the matrix amplifier 56, as shown, the gating unit 78will convert any output from the matrix 56 which is not zero into anautomatic chroma control signal for application to the amplifying system62 to set the chrominance channel gain.

Using the pedestal of the color reference signal as the measure fordeveloping this control signal instead of focusing on the energy contentof the color synchronizing burst obviates many of the previousdifficulties existent in prior designs where the cumulative tolerancesassociated with the burst amplitude deleteriously affected thisautomatic gain control of the chroma amplifiers. A second advantage ofutilizing a color reference signal of the type described in providingsaturation control follows from a realization that should the contrastcontrol of the receiver be adjusted, a correction voltage ofcorresponding polarity will be developed to adjust the chrominance gainin like manner. Automatic tracking is thus achieved without the need forany common coupling action between the control employed and theluminance and chrominance portions of the receiver.

A manual saturation control can be included in the apparatus of FIG. 3by utilizing a phase splitter 80 coupled to the output of thecoincidence gate 76, and by adjusting its variable output arm 81 toproduce either a positive or negative pulse in time synchronism with thecolor reference signal and, preferably, derived from it. Such pulsesignal can simulate an error signal of the type described in conjunctionwith the matrix 56, and can cause the automatic chroma control circuitto vary the chrominance gain in appropriate manner when the pulse signalis coupled to the amplifier system 62 by the conductor 82.

The burst amplifier 64 and reference oscillator 50 are additionallyshown as being coupled to a phase detector 84 for developing a controlvoltage which, when applied via a color killer amplifier 86 to thechroma amplifying system 62, will de-activate the chrominance channeland eliminate the possibility of color "noise" being displayed on thecathode-ray kinescope during monochrome reception. Each of the unitsshown in FIG. 3 are either readily available devices, or ones which caneasily be constructed by one skilled in the art.

While there has been described what is considered to be a preferredembodiment of the present invention, it will be readily apparent thatmodifications may be made without departing from the spirit and scope ofthe instant disclosure. Thus, while the color reference signal has beendescribed as being of --(R-Y) phase, it will be recognized that a phaseof --(B-Y) might be used as well, and still utilize the teachingsherein. With such modification, it will be noted that the automaticphase control (APC) signal for hue correction would be developed througha sensing of the output of the R-Y demodulator 52 instead of the B-Ydemodulator 54. It will similarly be noted that the automatic chromacontrol (ACC) signal for saturation correction would be developed bysensing the output of the blue matrix 58, rather than the red matrix 56.

This use of a vertical reference signal at the receiver to improve thequality of operation and the consistency of a reproduced colorrepresents one step further than that recently proposed by the BroadcastTelevision Systems Committee of the Electronic Industries Association.There, although a color reference signal was inserted into the verticalblanking interval for reducing errors in reproduced hue and saturation,the signal was utilized in adjusting the phase and amplitude of thetransmitted chrominance signal and the level of color burst, amongstothers, so as to radiate a signal corresponding to the one which wasoriginated in the video system where the correct amplitude and phase ofthe composite signal was established. As will be readily appreciated,such phenomena as multipath, transmission line reflection anddifferential phase errors could very will upset these relationships intransmission to the receiver. Although such use of a vertical intervalreference signal (VIR) could very well lessen those characteristics oftelevision studio and network operation which adversely affect hue andsaturation, the apparatus of the invention goes one step beyond inutilizing these reference signals to offset many of the disturbancesduring transmission which would otherwise reduce the benefits suchcertification would provide.

What is claimed is:
 1. In a color television receiver adapted to receivea television signal including a luminance component, a chrominancecomponent modulated in both phase and amplitude, periodically recurringcolor synchronizing bursts occupying prescribed intervals during thehorizontal retrace portions of said signal and a color reference signal.Iadd.fully .Iaddend.occupying a prescribed interval during the verticalretrace portion of said signal, apparatus comprising:first means forproviding an oscillatory signal to demodulate said chrominance component.[.and produce color difference signals containing informationproportional to the hue and saturation of the televised scene.]..Iadd.second means including at least first and second chrominancesignal demodulators responsive to said oscillatory signal, and alsoresponsive to said television signal, for demodulating said chrominancecomponent and producing color difference signal outputs representativeof the hue and saturation of the televised scene, said reference signalbeing in quadrature phase relationship with respect to the demodulationaxis associated with said first demodulator.Iaddend.; .[.second.]..Iadd.third .Iaddend.means responsive to said television signal forrecovering the color synchronizing bursts thereof and for coupling saidbursts to said first means to lock at least the frequency of theoscillatory signal provided thereby to the frequency of such bursts; and.[.third.]. .Iadd.fourth .Iaddend.means, also responsive to saidtelevision signal, for recovering said color reference signal and forutilizing said signal to develop a control signal for said first meansto adjust the phase of said oscillatory signal as a function of saidreference signal.Iadd., said fourth means comprising the combination of(a) a frequency selective amplifier for delivering said chrominance andcolor reference signal components of said television signal to saiddemodulators, (b) said first demodulator, and (c) means for sensing theoutput of said first demodulator during the occurrence of said referencesignal and deriving said control signal therefrom.Iaddend.; whereby thedegree of error in the hue of a reproduced color image attributable tosuch transmission characteristics as multipath, transmission linereflection and the like is correspondingly reduced.[...]. .Iadd.whereinthere is additionally included fifth means, responsive to said deliveryof said color reference signal to said second demodulator via saidamplifier, for controlling the amplitude of said color differencesignals and the saturation of the reproduced color image as a functionof departures of the amplitude of said delivered reference signal from areference level responsive to the luminance component level exhibitedduring said prescribed interval. .Iaddend.
 2. .[.The apparatus of claim1.]. .Iadd.In a color television receiver adapted to receive atelevision signal including a luminance component, a chrominancecomponent modulated in both phase and amplitude, periodically recurringcolor synchronizing bursts occupying prescribed intervals during thehorizontal retrace portions of said signal and a color reference signaloccupying a prescribed interval during the vertical retrace portion ofsaid signal, apparatus comprising:first means for providing anoscillatory signal to demodulate said chrominance component; secondmeans including at least first and second chrominance signaldemodulators responsive to said oscillatory signal, and also responsiveto said television signal, for demodulating said chrominance componentand producing color difference signal outputs representative of the hueand saturation of the televised scene, said reference signal being inquadrature phase relationship with respect to the demodulation axisassociated with said first demodulator; third means responsive to saidtelevision signal for recovering the color synchronizing bursts thereofand for coupling said bursts to said first means to lock at least thefrequency of the oscillatory signal provided thereby to the frequency ofsuch bursts; and fourth means also responsive to said television signal,for recovering said color reference signal and for utilizing said signalto develop a control signal for said first means to adjust the phase ofsaid oscillatory signal as a function of said reference signal, saidfourth means comprising the combination of (a) a frequency selectiveamplifier for delivering said chrominance and color reference signalcomponents of said television signal to said demodulators, (b) saidfirst demodulator, and (c) means for sensing the output of said firstdemodulator during the occurrence of said reference signal and derivingsaid control signal therefrom; whereby the degree of error in the hue ofa reproduced color image attributable to such transmissioncharacteristics as multipath, transmission line reflection and the likeis correspondingly reduced; and wherein there is additionally includedfifth means, responsive to said delivery of said color reference signalto said second demodulator via said amplifier, for controlling theamplitude of said color difference signals and the saturation of thereproduced color image as a function of departures of the amplitude ofsaid delivered reference signal from a reference level responsive to theluminance component level exhibited during said prescribed interval; and.Iaddend.wherein .[.there is additionally included fourth means forcoupling the chrominance component of said television signal fordemodulation with said oscillatory signal to produce said colordifference signals, and wherein fifth means is also included to respondto corresponding coupling of said color reference signal via said fourthmeans to control the amplitude of said color difference signals and thesaturation of the reproduced color image as a function of the amplitudeof said reference signal.]. .Iadd.said fifth means includes means formatrixing the output of said second demodulator with said luminancecomponent, means responsive to the output of said matrixing means duringsaid color reference signal occurrence for developing a gain controlvoltage, and means for utilizing said gain control voltage to controlthe gain of said amplifier .Iaddend..
 3. The apparatus of claim 2wherein .[.sixth.]. .Iadd.seventh .Iaddend.means is also included,coupled to said first, .[.second.]. .Iadd.third .Iaddend.and fourthmeans, respectively, and responsive to the presence of said providedoscillatory signal and to said recovered color synchronizing bursts todisable said fourth .[.means.]. .Iadd.amplifier .Iaddend.during themonochrome transmission of a televised scene and in the absence of saidsynchronizing bursts. .[.4. The apparatus of claim 2 wherein said secondmeans couples the recovered color synchronizing bursts to said firstmeans to lock the frequency of said oscillatory signal to the frequencyof said synchronizing bursts and wherein said third means couples saidcontrol signal to said first means to lock the phase of said oscillatorysignal to the phase of said color reference signal..].
 5. The apparatusof claim 4 wherein said .[.first.]. .Iadd.sixth .Iaddend.means.[.includes a reactance control device responsive to alternating currentsignals to regulate the frequency of said provided oscillatory signalsand to direct current signals to regulate the phase of said oscillatorysignals, wherein said second means alternating current couples therecovered color synchronizing burst to said reactance control device andwherein said third means direct current couples said control signal tosaid reactance device.]. .Iadd.comprises means for modifying one of thesignal inputs to said matrixing means, said signal input modifying meansincluding a potentiometer with a tap subject to manual adjustment of itsposition to control the modification of said one signal input in suchmanner that the existence, magnitude and sense of said simulatedsaturation error is dependent upon the position of adjustment of saidtap.Iaddend..
 6. The apparatus of claim 5 for use in a color televisionreceiver providing color difference signals along R-Y and B-Ydemodulation axes and operative with a television signal including saidcolor reference signal at --(R-Y) phase, wherein said .[.third meansincludes.]. .Iadd.sensing .Iaddend.means .[.for monitoring.]..Iadd.monitors .Iaddend.the amplitude of the color difference signalsprovided along said B-Y demodulation axis and .[.to develop.]..Iadd.develops .Iaddend.said control signal for said first means toadjust the phase of said oscillatory signal to reduce the amplitude ofsaid B-Y color difference signal .Iadd.output during said colorreference signal occurrence .Iaddend.in a direction to automaticallycompensate for transmission characteristic changes as would adverselyaffect the hue of the reproduced color image.
 7. The apparatus of claim5 for use in a color television receiver providing color differencesignals along B-Y and R-Y demodulation axes and operative with atelevision signal including said color reference signal at --(B-Y)phase, wherein said .[.third means includes.]. .Iadd.sensing.Iaddend.means .[.for monitoring.]. .Iadd.monitors .Iaddend.theamplitude of the color difference signals provided along said R-Ydemodulation axis and .[.to develop.]. .Iadd.develops .Iaddend.saidcontrol signal for said first means to adjust the phase of saidoscillatory signal to reduce the amplitude of said R-Y color differencesignal .Iadd.output during said color reference signal occurrence.Iaddend.in a direction to automatically compensate for transmissioncharacteristic changes as would adversely affect the hue of thereproduced color image.
 8. The apparatus of claim 6 wherein said.[.fifth means includes means for monitoring the amplitude of the colordifference signal provided.]. .Iadd.second demodulator effectsdemodulation .Iaddend.along said R-Y demodulation axis .[.and to developsaid control signal for said fourth means to adjust the gain thereof toreduce the amplitude of said R-Y color difference signal in a directionto automatically compensate for transmission characteristic changes aswould adversely affect the saturation of the reproduced color image.]..9. The apparatus of claim .[.6.]. .Iadd.7 .Iaddend.wherein said .[.fifthmeans includes means for monitoring the amplitude of the colordifference signal provided.]. .Iadd.second demodulator effectsdemodulation .Iaddend.along said B-Y demodulation axis .[.and to developsaid control signal for said fourth means to adjust the gain thereof toreduce the amplitude of said B-Y color difference signal in a directionto automatically compensate for transmission characteristic changes aswould adversely affect the saturation of the reproduced color image.]...Iadd.10. The apparatus of claim 2 also including sixth means forselectively causing said matrixing means to provide an output duringsaid prescribed interval which is inclusive of a component simulating asaturation error of controllable magnitude and sense so as to effect adesired modification of the saturation of a color reproduction of saidtelevised scene effected in response to said color difference signalsand said luminance component. .Iaddend. .Iadd.11. In a color televisionreceiver adapted to receive a television signal including a luminancecomponent, a chrominance component comprising a color subcarriermodulated in both phase and amplitude, periodically recurring colorsynchronizing bursts occupying prescribed intervals during thehorizontal retrace portions of said signal and a color reference signal,of color subcarrier frequency and of a reference phase and amplitude,occupying prescribed interval during the vertical retrace portion ofsaid signal, apparatus comprising:first means for providing anoscillatory signal to demodulate said chrominance component and producecolor difference signals containing information proportional to the hueand saturation of the televised scene; second means responsive to saidtelevision signal for recovering the color synchronizing burststherefrom and for coupling said bursts to said first means to lock atleast the frequency of the oscillatory signal provided thereby to thefrequency of such bursts; third means, also responsive to saidtelevision signal, for recovering said color reference signal and forutilizing said signal to develop a control signal for said first means;said third means comprising (a) an amplifier for said chrominance andcolor reference signal components of said television signal, (b) a firstchrominance component demodulator responsive to respective outputs ofsaid first means and said amplifier and effecting demodulation of saidmodulated color subcarrier along a demodulation axis in quadraturerelationship to said reference phase to develop a first color differencesignal, and (c) means for sensing the output of said first demodulatorduring said prescribed vertical retrace interval for developing saidcontrol signal for said first means to adjust the phase of saidoscillatory signal as a function of the phase of said reference signal;and fourth means responsive to respective outputs of said first meansand said amplifier for controlling the amplitude of said colordifference signals and the saturation of the reproduced color image viaadjustment of the gain of said amplifier as a function of the amplitude,with respect to a reference level, of said amplified reference signal;said fourth means comprising a second chrominance component demodulatorresponsive to outputs of said first means and said amplifier andeffecting demodulation of said modulated color subcarrier along a seconddemodulation axis in quadrature relationship to said first demodulationaxis to develop a second color difference signal, means for matrixingthe output of said second demodulator with said luminance component,means responsive to the output of said matrixing means during saidprescribed vertical retrace interval for developing a gain controlvoltage, and means for utilizing said gain control voltage to controlthe gain of said amplifier; said reference level being responsive to thelevel of said luminance component supplied to said matrixing meansduring said prescribed vertical retrace interval; and wherein thecolor-difference signals developed by said first and second demodulatorsin response to said chrominance component are utilized in development ofa color reproduction of said televised scene. .Iaddend. .Iadd.12.Apparatus in accordance with claim 11 also including fifth means forselectively causing said matrixing means to provide an output duringsaid prescribed vertical retrace interval which is inclusive of acomponent simulating a saturation error of controllable magnitude andsense so as to effect a desired modification of the saturation of saidcolor reproduction of said televised scene. .Iaddend. .Iadd.13.Apparatus in accordance with claim 12 wherein said fifth means comprisesmeans for modifying one of the signal inputs to said matrixing means,said signal input modifying means including a potentiometer with a tapsubject to manual adjustment of its position to control the modificationof said one signal input in such manner that the existence, magnitudeand sense of said simulated saturation error is dependent upon theposition of adjustment of said tap. .Iaddend. .Iadd.14. In a colortelevision receiver adapted to receive a television signal including aluminance component having a given level representative of black, achrominance component comprising a color subcarrier modulated in bothphase and amplitude, periodically recurring color synchronizing burstsoccupying prescribed intervals during the horizontal retrace portions ofsaid signal and a color reference signal, of color subcarrier frequencyand of a reference phase and amplitude, occupying a prescribed intervalduring the vertical retrace portion of said signal and superimposed upona pedestal shifted in the white direction from said black representativelevel, apparatus comprising:first means for providing an oscillatorysignal to demodulate said chrominance component and produce colordifference signals containing information proportional to the hue andsaturation of the televised scene; second means responsive to saidtelevision signal for recovering the color synchronizing burststherefrom and for coupling said bursts to said first means to lock atleast the frequency of the oscillatory signal provided thereby to thefrequency of such bursts; third means, also responsive to saidtelevision signal, for recovering said color reference signal and forutilizing said signal to develop a control signal for said first means;said third means comprising the combination of (a) a frequency selectiveamplifier for amplifying the chrominance and color reference signalcomponents of said television signal, (b) a first chrominance componentdemodulator responsive to respective outputs of said first means andsaid amplifier and effecting demodulation of said modulated colorsubcarrier along a demodulation axis in quadrature relationship to saidreference phase to develop a first color difference signal, and (c)means for sensing the output of said first demodulator during saidprescribed vertical retrace interval for developing said control signalfor said first means to adjust the phase of said oscillatory signal as afunction of the phase of said reference signal; a second chrominancecomponent demodulator responsive to respective outputs of said firstmeans and said amplifier and effecting demodulation of said modulatedcolor subcarrier along a second demodulation axis in quadraturerelationship to said first demodulation axis to develop a secondcolor-difference signal; means for matrixing the output of said seconddemodulator with a signal which is representative of said pedestalduring said prescribed vertical retrace interval; means responsive tothe output of said matrixing means during said prescribed verticalretrace interval for developing a gain control voltage; and means forutilizing said gain control voltage to control the gain of saidamplifier; wherein the color-difference signals developed by said firstand second demodulators in response to said chrominance component areutilized in development of a color reproduction of said televised scene..Iaddend.